The human eye sees color as a result of three types of receptors, called cones, listed in the chart below. A range of wavelengths of light stimulates each of these receptor types to varying degrees. Yellowish-green light, for example, stimulates both L and M cones equally strongly, but only stimulates S-cones weakly; red light stimulates L cones much more than M cones, and S cones hardly at all; blue-green light stimulates M cones more than L cones, and S cones a bit more strongly; and blue light stimulates S cones more strongly than red or green light, but L and M cones more weakly. The brain combines the information from each type of receptor to give rise to different perceptions (i.e., colors) of different wavelengths of light.
Cone typeNameRangePeak wavelengthSB400-500 nm420-440 nmMΓ450-630 nm534-555 nmLP500-700 nm564-580 nm
Test procedures such as optical computed tomography (OCT), visual field analyzers, etc., are used primarily to screen and diagnose specific eye disease. OCTs and visual field analyzers are tests generally used once the patient is symptomatic, well after permanent eye damage has occurred.
A test, called the Cone Contrast Test (CCT), is used to determine deficiencies of these cones in an individual's eye. The CCT is explained in greater detail in the published articles titled “Rapid Quantification of Color Vision: The Cone Contrast Test” by Rabin et al. published in Investigative Ophthalmology & Visual Science, February 2011, Vol. 52, No. 2, and “Quantification of Color Vision with Cone Contrast Sensitivity” by Jeff Rabin (2004), 21, pp. 483-485, the disclosures of which are hereby incorporated by reference.
The CCT is a functional test, making it a broad, non-disease-specific test. These features make CCT an affordable screening tool able to detect cone sensitivity degradation associated with a broad spectrum of disease/toxicity early enough to, with treatment, potentially prevent permanent eye damage. The CCT may also be used as a predictive test for eye systemic, and neurological disease and retinal toxicity, as well as a monitoring test for disease/toxicity progression and treatment.
Consistent calibration of a color display monitor for administering the CCT is needed. Additionally, a low cost calibration system is needed due to inconsistent calibration over time. With standard “off-the-shelf” colorimeters, interference from other software, including software produced by Microsoft Corporation, override calibration values and render the test invalid.